The fabrication of semiconductor devices involves forming electronic components in and on semiconductor substrates, such as silicon wafers. These electronic components may include conductive layers, insulation layers, and/or implanted dopants, which are used to achieve specific electrical properties.
The fabrication process includes etching of the wafer to remove material therein. Wet etching involves applying chemicals, such as buffered hydrofluoric acid, to the wafer in order to react with the substrate and facilitate the etching process. Plasma etching, also referred to as “dry etching,” uses a source gas of charged particles in an applied electric field to accelerate the charged particles toward the wafer. The charged particles may either react chemically with the wafer material (substrate) to etch the substrate, or the physical collisions between the charged particles and the wafer can sputter substrate atoms from the surface of the wafer, resulting in etching.
Reactive-ion etching is a type of plasma etching. In a reactive-ion etching tool, the semiconductor wafer is placed on a charged surface, called a chuck, which electrostatically clamps the wafer in place. The chuck also serves as a heat sink for the system. As the charged particles in the plasma react with the substrate, heat is generated and transferred away from the wafer using a cooling gas, such as helium, which flows through channels carved into the surface of the chuck. As a result, the capacitive coupling between the chuck and the wafer is not constant, which can lead to complications in the etching process.